| Message ID | 20210922000533.713300-10-seanjc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | perf: KVM: Fix, optimize, and clean up callbacks | expand |
On 22/09/21 02:05, Sean Christopherson wrote: > Use static_call to optimize perf's guest callbacks on arm64 and x86, > which are now the only architectures that define the callbacks. Use > DEFINE_STATIC_CALL_RET0 as the default/NULL for all guest callbacks, as > the callback semantics are that a return value '0' means "not in guest". > > static_call obviously avoids the overhead of CONFIG_RETPOLINE=y, but is > also advantageous versus other solutions, e.g. per-cpu callbacks, in that > a per-cpu memory load is not needed to detect the !guest case. > > Based on code from Peter and Like. > > Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Cc: Like Xu <like.xu.linux@gmail.com> > Signed-off-by: Sean Christopherson <seanjc@google.com> > --- > include/linux/perf_event.h | 28 ++++++---------------------- > kernel/events/core.c | 15 +++++++++++++++ > 2 files changed, 21 insertions(+), 22 deletions(-) > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index eefa197d5354..d582dfeb4e20 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -1240,37 +1240,21 @@ extern void perf_event_bpf_event(struct bpf_prog *prog, > > #ifdef CONFIG_GUEST_PERF_EVENTS > extern struct perf_guest_info_callbacks *perf_guest_cbs; > -static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void) > -{ > - /* Reg/unreg perf_guest_cbs waits for readers via synchronize_rcu(). */ > - lockdep_assert_preemption_disabled(); > +DECLARE_STATIC_CALL(__perf_guest_state, *perf_guest_cbs->state); > +DECLARE_STATIC_CALL(__perf_guest_get_ip, *perf_guest_cbs->get_ip); > +DECLARE_STATIC_CALL(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr); > > - /* Prevent reloading between a !NULL check and dereferences. */ > - return READ_ONCE(perf_guest_cbs); > -} > static inline unsigned int perf_guest_state(void) > { > - struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); > - > - return guest_cbs ? guest_cbs->state() : 0; > + return static_call(__perf_guest_state)(); > } > static inline unsigned long perf_guest_get_ip(void) > { > - struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); > - > - /* > - * Arbitrarily return '0' in the unlikely scenario that the callbacks > - * are unregistered between checking guest state and getting the IP. > - */ > - return guest_cbs ? guest_cbs->get_ip() : 0; > + return static_call(__perf_guest_get_ip)(); > } > static inline unsigned int perf_guest_handle_intel_pt_intr(void) > { > - struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); > - > - if (guest_cbs && guest_cbs->handle_intel_pt_intr) > - return guest_cbs->handle_intel_pt_intr(); > - return 0; > + return static_call(__perf_guest_handle_intel_pt_intr)(); > } > extern void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs); > extern void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs); > diff --git a/kernel/events/core.c b/kernel/events/core.c > index c6ec05809f54..79c8ee1778a4 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -6485,12 +6485,23 @@ static void perf_pending_event(struct irq_work *entry) > #ifdef CONFIG_GUEST_PERF_EVENTS > struct perf_guest_info_callbacks *perf_guest_cbs; > > +DEFINE_STATIC_CALL_RET0(__perf_guest_state, *perf_guest_cbs->state); > +DEFINE_STATIC_CALL_RET0(__perf_guest_get_ip, *perf_guest_cbs->get_ip); > +DEFINE_STATIC_CALL_RET0(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr); > + > void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) > { > if (WARN_ON_ONCE(perf_guest_cbs)) > return; > > WRITE_ONCE(perf_guest_cbs, cbs); > + static_call_update(__perf_guest_state, cbs->state); > + static_call_update(__perf_guest_get_ip, cbs->get_ip); > + > + /* Implementing ->handle_intel_pt_intr is optional. */ > + if (cbs->handle_intel_pt_intr) > + static_call_update(__perf_guest_handle_intel_pt_intr, > + cbs->handle_intel_pt_intr); > } > EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks); > > @@ -6500,6 +6511,10 @@ void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) > return; > > WRITE_ONCE(perf_guest_cbs, NULL); > + static_call_update(__perf_guest_state, (void *)&__static_call_return0); > + static_call_update(__perf_guest_get_ip, (void *)&__static_call_return0); > + static_call_update(__perf_guest_handle_intel_pt_intr, > + (void *)&__static_call_return0); > synchronize_rcu(); > } > EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks); > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index eefa197d5354..d582dfeb4e20 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -1240,37 +1240,21 @@ extern void perf_event_bpf_event(struct bpf_prog *prog, #ifdef CONFIG_GUEST_PERF_EVENTS extern struct perf_guest_info_callbacks *perf_guest_cbs; -static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void) -{ - /* Reg/unreg perf_guest_cbs waits for readers via synchronize_rcu(). */ - lockdep_assert_preemption_disabled(); +DECLARE_STATIC_CALL(__perf_guest_state, *perf_guest_cbs->state); +DECLARE_STATIC_CALL(__perf_guest_get_ip, *perf_guest_cbs->get_ip); +DECLARE_STATIC_CALL(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr); - /* Prevent reloading between a !NULL check and dereferences. */ - return READ_ONCE(perf_guest_cbs); -} static inline unsigned int perf_guest_state(void) { - struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); - - return guest_cbs ? guest_cbs->state() : 0; + return static_call(__perf_guest_state)(); } static inline unsigned long perf_guest_get_ip(void) { - struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); - - /* - * Arbitrarily return '0' in the unlikely scenario that the callbacks - * are unregistered between checking guest state and getting the IP. - */ - return guest_cbs ? guest_cbs->get_ip() : 0; + return static_call(__perf_guest_get_ip)(); } static inline unsigned int perf_guest_handle_intel_pt_intr(void) { - struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs(); - - if (guest_cbs && guest_cbs->handle_intel_pt_intr) - return guest_cbs->handle_intel_pt_intr(); - return 0; + return static_call(__perf_guest_handle_intel_pt_intr)(); } extern void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs); extern void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs); diff --git a/kernel/events/core.c b/kernel/events/core.c index c6ec05809f54..79c8ee1778a4 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6485,12 +6485,23 @@ static void perf_pending_event(struct irq_work *entry) #ifdef CONFIG_GUEST_PERF_EVENTS struct perf_guest_info_callbacks *perf_guest_cbs; +DEFINE_STATIC_CALL_RET0(__perf_guest_state, *perf_guest_cbs->state); +DEFINE_STATIC_CALL_RET0(__perf_guest_get_ip, *perf_guest_cbs->get_ip); +DEFINE_STATIC_CALL_RET0(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr); + void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) { if (WARN_ON_ONCE(perf_guest_cbs)) return; WRITE_ONCE(perf_guest_cbs, cbs); + static_call_update(__perf_guest_state, cbs->state); + static_call_update(__perf_guest_get_ip, cbs->get_ip); + + /* Implementing ->handle_intel_pt_intr is optional. */ + if (cbs->handle_intel_pt_intr) + static_call_update(__perf_guest_handle_intel_pt_intr, + cbs->handle_intel_pt_intr); } EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks); @@ -6500,6 +6511,10 @@ void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs) return; WRITE_ONCE(perf_guest_cbs, NULL); + static_call_update(__perf_guest_state, (void *)&__static_call_return0); + static_call_update(__perf_guest_get_ip, (void *)&__static_call_return0); + static_call_update(__perf_guest_handle_intel_pt_intr, + (void *)&__static_call_return0); synchronize_rcu(); } EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
Use static_call to optimize perf's guest callbacks on arm64 and x86, which are now the only architectures that define the callbacks. Use DEFINE_STATIC_CALL_RET0 as the default/NULL for all guest callbacks, as the callback semantics are that a return value '0' means "not in guest". static_call obviously avoids the overhead of CONFIG_RETPOLINE=y, but is also advantageous versus other solutions, e.g. per-cpu callbacks, in that a per-cpu memory load is not needed to detect the !guest case. Based on code from Peter and Like. Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Like Xu <like.xu.linux@gmail.com> Signed-off-by: Sean Christopherson <seanjc@google.com> --- include/linux/perf_event.h | 28 ++++++---------------------- kernel/events/core.c | 15 +++++++++++++++ 2 files changed, 21 insertions(+), 22 deletions(-)